1. Field of the Invention
This invention relates to a vascular prosthesis composed of a porous tubing of polytetrafluoroethylene (to be abbreviated "PTFE"), and aims at increasing the anti-coagulating property of its inner surface, preventing bleeding, and is directed to increasing the strength of the tubing and improving the ability of its outside surface to connect with the tissues of a patient.
2. Description of the Prior Art
Many reports have been made heretofore to show that a porous tubing of PTFE produced by a stretching method can be clinically used as a vascular prosthesis. Such a prosthesis is regarded as better than conventional vascular prosthesis made of knitted or woven fabrics. A PTFE tubing which has been subjected to a stretching treatment has a microstructure composed of very fine fibers and nodes connected to one another by these fibers. The diameters of the fibers vary depending on stretching conditions, but can be made much smaller than those of the fibers of the knitted or woven fabrics mentioned above. Moreover, since the pore diameter and porosity of the tubing can be varied freely, when it is used as an artificial vessel, it is pliable and scarcely permits formation of thrombus. The tubing also shows good formation of a neointima on its inner surface without any appreciable adverse effect on the surrounding tissues. Thus, the stretched PTFE tubing is regarded as one of the best vascular prostheses.
However, the porous PTFE tubing of PTFE produced by stretching is not completely free from formation of thrombus and still has room for improvement. The stretched PTFE tubing also has the disadvantage that when it is used as a vascular prosthesis and joined with the living body, the needle or suture tends to tear the tubing. Moreover, it is difficult for natural occlusion of suture holes to occur based on the elasticity of the porous PTFE tubing alone, and bleeding from the suture holes is sometimes noted after the junction operation. Another problem is the low ability of the outside surface of the porous PTFE tubing to connect with the surrounding tissues of a patient.
The present invention offers a solution to these problems.